This invention relates to a magnetic disk unit for data storage, and more particularly to a mechanism for preventing a magnetic head in the disk unit from making direct contact with a data storage surface of the associated disk.
In conventional magnetic disk units for data storage, a magnetic head for read/write operations on a data storage surface of a rotating disk is attached to a suspension arm which flies on a thin cushion of air, or air-bearing, created above the rotating disk. To maintain an appropriate clearance between the head and the rotating disk by counterbalancing the air-cushioning force the suspension arm applies loading force to the head so as to urge the head toward the disk. Therefore, when the disk stops rotating the head comes into contact with the disk surface.
Recently there is a trend toward a decrease in the head-disk clearance for the purpose of enhancing the data storage density and thereby increasing the data storage capacity of each disk. To comply with such a trend recent magnetic disks have been improved in surface smoothness, but as an unfavorable effect of the improvement it is not rarely that a head sticks to a disk surface during stationary contact of the head with the disk.
Relatively simple countermeasures to the sticking phenomenon are supplying a large current to a spindle motor installed in a magnetic disk unit for rotating magnetic disks thereby augmenting the generated torque or supplying a large current to a voice coil motor in order to forcibly overcome the sticking. However, these countermeasures are against the requirement for saving of electric power and unsuitable for small-sized computers such a s personal computers of lap-top type using batteries for driving magnetic disk units. Besides, forcible detachment of a sticking head from the disk is liable to damage the disk and/or the head.
As a measure for solving the sticking problem there are proposals of restraining a magnetic head from freely moving toward the associated disk by employing a link mechanism to load the head when the disk is rotating and unload the head when the disk stops rotating. Besides, it has been proposed to keep a magnetic head at a predetermined distance from the associated disk surface when the disk is not rotating by forming a sloped face around the periphery of the disk and shaping the suspension of the head so as to engage and slides on the sloped face. However, the link mechanism is intricate and costly and hence is unsuitable for small-sized disk units used in, for example, personal lap-top computers. The mechanism using a sloped face around the periphery of the disk has a drawback that in the loading and unloading operations the motion of the head becomes oblique with respect to the data storage surface of the disk, not simply vertical to the disk. Due to such motion of the head the loading and unloading positions becomes somewhat indefinite, and there is a problem as to the state of access of the head to the disk.
Meanwhile, magnetic disk units for personal lap-top computers are required to endure shocks that may be applied thereto while the computers are being carried. It is usual to prevent each magnetic head from beating the associated disk surface by augmenting the force to urge the head toward the disk and/or to reduce the weight of each head in order not to seriously damage the associated disk even if the head beats the disk. However, by strongly pressing the head against the disk it is inevitable that friction between the head and the disk increases, and hence large electric power is consumed at the start of rotation of the disk. Therefore, this measure is not very suitable for magnetic disc units in personal lap-top computers. A reduction in the head weight is not always sufficient for realizing desired shock resistance.